Urea-formaldehyde condensation products



Patented Dec. 20, 1938 PATENT OFFICE UREA-FOWLDEHYDE CONDENSATION mowersLeonard Smidth, New'York, N. Y.

No Drawing.

This invention relates to the reaction products of urea or equivalentsubstances with formaldehyde or equivalent substances. It relatesParticularly to those products which may be cast, molded or machined orotherwise'treated to make shaped articles and also tovarnishes,lacquers, paints and enamels containing such synthetic products. IAccordlng'to the prior art the reaction between M urea and formaldehydecan be roughly divided into three stages, the condensation stage, thepolymerization stage, and the hardening stage. (See Ripper U. S. Pat.No. 1,687,312; page 1, line 3.) The condensation stage is usuallycompleted after a comparatively short reaction of urea and formaldehyde,either boiling of the reactants or use-of a lower temperature for acorrespondingly longer time. Prior workers have shown that thepolymerization stage is usually a prolonged one and is usually conductedby boil-. ing. The viscosity gradually rises as boiling is continueduntil the product does not become cloudy on cooling. For the manufactureof glass-like materials the product is then vacuum distilled so as toremove as much water as possible before'belng cast. The hardening stageis the one in which the casting liquid is changed in the mold into thefinal infusible insoluble material. This is accomplished by heatingeither with or without pressure.

In copending application No. 429,202, filed Feb. 17,1930, I show how tomake a superior urea formaldehyde molding composition by reacting ureaand formaldehyde so as not to carry it beyo d the condensation stage'andthen simultaneously car.- rying on the reaction and drying. This is doneby reacting urea and formaldehyde at a low temperature in thepresence ofpotentially acid substances and removing water that is present or formedat a low temperature simultaneously with the reaction. The finalpolymerization or hardening stage is carried out at a higher tein'pera-Application August 10, 1933, Serial No. 684,581

yield free hydrogen ions. These substances may be ammonia; ammoniumsalts; salts which hydrolyze in solution to yield free hydrogen ions,such as zinc chloride; water soluble esters, such as methyl formate; andorganic compounds, such 5 as formamide. V

Commercial formaldehyde usually contains acidic'material, mostly formicacid, in sufficient quantity to establish a concentration of hydrogenion ofpI-I 3. This concentration of acidic cata- 10 lyst is sufficientlyhigh to carry the reaction so rapidly that the product is of littlevalue. Ammonia is therefore aided to reduce the acidity from theconcentration of pH 3 to between pH 4 and pH 7.5. Now I have found thatno apparent 15 change occurs if formaldehyde with added ammonia remainsat normal temperature. However, above 40 C. a reaction occurs, the rateof which increases with increase of temperature. The hydrogen ionconcentration is observed to change 20 slowly at first, then rapidly,and then more slowly. The rate of change depends on the temperature andthe hydrogen ion concentration of the original formaldehyde ammoniasolution. The same phenomena were observed when the formaldehydeammonia. solution contained the pro-per amount of urea desired for thecondensation. It is believed that the ammonia reacts with freeformaldehyde with the formation of hexamethylenetetramine and theconsequent liberation of the original formic acid, thus increasing thehydrogen ion concentration. This increasing catalyst hydrogen ionaccelerates the formation of the -flnal products with the consequentliberation of formaldehyde. The formaldehyde thus produced reacts withany ammonia or urea that might be present. The control of thetemperature of this reacting mixture makes possible a. great improvementin the process and in the quality and uniformity of the moldingcomposition.

I have made a urea formaldehyde mixture in the mole ratio of 1.25 and 2respectively with ammonia or other bases added to bring the hydrogen ionconcentration of the solution to pH 6.5 and have held this solution atabout 30 C. for about thirty minutes. It was then mixed with paper orother filler and subjected at once to a stream of dry air for some hoursat normal temperature. When sufficient water is removed the material canbe heated to a higher temperature 5 until dry. I have found thatmaterial so produced is uniform in its properties.

When other substances than ammonia or ammonium salts are used to givefree hydrogen ions and thus catalyze the reaction, the original acidityof the formaldehyde solution can be reduced by the use of sodiumhydroxide or other alkalis.

The composition is finally subjected in the mold to the action of heatand pressure. The high temperature, say between C. and C. continuestheprocess that was retarded by the low temperature of the preparationprocess described (with the formation of hexamethylenetetramine andconsequently rapid increase in the amount of acid catalyst present).Hence, an initial good flow is obtained. In case a salt of ammonia and astronger acid than formic acid such as HCl is added, with the properadjustment of the hydrogen ion as described above to give satisfactoryhydrogen ion concentration as before, i. e., between pH4 and pH7.5, thenthe formation of hexamethylenetetramine results in the liberation of thestronger acid and the consequent more rapid increase in hydrogen ionresults in a shorter curing time.

The above procedure yields a uniform product that is high in finalinfusible insoluble material and low in free formaldehyde both of whichare factors that determine the strength and the resistance to waterabsorption.

The essence of the above and the present invention is that the reactionis not carried beyond the condensation stage before the water is begunto be taken off, and proceeds in such a manner that as much of the waterpresent or formed is removed as soon as possible either before or duringthe reaction and drying process. A potentially acidic substance is usedso as to keep the initial pH value sufiiciently high so that the productwill remain clear, and yet furnish additional acid to speed up thepolymerization and hardening stage. During the condensation period Ihave shown in my U. S. Patent #1,893,9l1 and in application #429,202that a pH value above 4 must be used in order to obtain a cleartransparent product. Otherwise if the reacting solution has a pH valueof less than 4 the product will be milky or cloudy. This is because withsuch a pH value the reaction will proceed so fast that a proper time isnot allowed for the formation of a colloidal solution, instead theproduct will tend to precipitate and will form a cloudy solution.Instead of using a potentially acidic substance the condensation can becarried out in either acid, neutral or basic medium just so that the pHvalue is above 4, and after the condensation either preferably adding anacid catalyst (acids, acidic salts, and acidic substances) or elsekeeping the polymerization stage on the acid side.

In preparing condensation products of urea and formaldehyde, thereaction stage is comparatively short. Instead of using a lowtemperature (30 C.) for a comparative longer time as is done in theabove specification, it is obvious that the same results can be attainedby using a higher temperature for the reaction; the higher thetemperature the shorter will be the time. In my U. S. Patent #1,893,911I show that the reaction state is probably represented by the formationof dimethylol urea. This is obtained by boiling the urea andformaldehyde for a few minutes. Anyhow the first or condensation stagecan be eliminated if instead of starting with urea and formaldehyde,dimethylol urea is used. It can be reacted and the water'taken oil as itis formed in the presence of an acid catalyst, with or withoutadditional urea being added to react with the formaldehyde as it isformed to give improved products.

It is very important that the proper amount of acids be used during thesecond or polymerization stage of the reaction. For some purposes suchas the preparation of glass-like materials, it is desirable to have asmuch acid present during the polymerization as possible because thegreater the amount present the quicker will be polymerization andhardening stages. However, if a stable intermediate product which mustbe kept for some time is desired, too much of an acid catalyst cannot beleft in the final product. For example, molding compositions must beprepared so that the reaction will not appreciably continue durinstorage or transit so that the composition will not lose its originalplasticity. Again it is desirable to have stable solutions for use aslacquers or cements which must keep for long periods of time withoutgelatinizing. In both of the above cases it is desirable to have the pH.on the acid side but as near the neutral point as possible say pH 6.5.If a larger amount of acid catalyst is present it must be neutralized togive such a pH value.

After the initial reaction and during the drying it is essential that aslittle water as possible is present; otherwise if a large amount of acidis present it will have a tendency to cause premature gelatinizatlon. Inthe absence of water the composition is rendered less sensitive to theaction of heat even though a comparatively large amount of acid catalystis present. It is a purpose of this invention to have as little waterpresent as pos sible during the polymerization stage so that instead ofgelatinizing, the product will more or less solidify substantiallywithout any or with very little water. The presence of acid substancesor catalysts aid in the polymerization and splitting oif of water. Ifthere is too much catalyst present the condensation product willgelatinire before all the water is removed, while if the solution is notsuillciently acid the final product obtained will be cloudy or milky.Therefore if the right conditions are obtained the final product,without fillers, will be clear and transparent. For some applications anabsolutely clear product is not necessary so that if approximateconditions herein set forth are observed the final material may be milkybut of superior physical properties. Ammonium salts are particularlyuseful for carrying out the invention because they tend to keep thesolution first at a high pH value during the condensation, then becomethe more acid on heatmg, such acidity being just the right rate so thata clear transparent final product can be prepared with ease.

In my U. S. Patent No. 1,893,911 I show how to obtain a cleartransparent product by adding urea in a proportion greater than 1.1moles of urea to 2 moles of formaldehyde. In copending application No.664,208, I show how to prepare molding compositions by reacting morethan 1.05 moles of urea to 2 moles of formaldehyde and use this materialto impregnate cellulose compounds. In carrying out this invention it ispreferable to use a proportion of greater than 1.05 moles of urea to 2moles of formaldehyde. Although it is easier to obtain clear transparentproducts by the use of lower proportions of urea than cor respond to1.05 moles of urea to 2 moles of formaldehyde, the final products willnot be as chemically resistant nor as strong. It is possible, however,to start with smaller proportion of urea and use conditions of reactionand drying under which the excess formaldehyde would be driven oil. Suchconditions would for example be attained in which the vacuumdistillation is carried out by using a high temperature in the bath anda mod- 1 erately high vacuum. Such a vacuum method is a convenient wayof carrying out the present invention. By using the method outlined inthe present application, it is possible to use a ratio of 1.5 moles ofurea with 1 mole for formaldehyde and obtain a clear transparentproduct.

The difference between this invention and prior ones is thatin the priorones-the polymerization or second stage is carried out by boiling orreacting the condensation product before the water is removed, whereasin the present invention as much of the solvent water and that formed byreaction is taken oif as soon as possible before or during the reactionand drying process. One method of removing the water from the productprepared according tothe above specification isto blow air through thecondensation product first at a normal temperature so as tosubstantially dry it, then heating the air blown through in order tocomplete the drying operation. This phase of my invention is set forthin my copending application #422,545 filed Jan..22, 1930.

Molded compositions such as those prepared in accordance with priorpractice from urea and formaldehyde are commonly molded under heat andpressure in the absence of an acid catalyst. A convenient method is tohave the acid catalyst present during the initial reaction between theurea and formaldehyde. The solution before setting isused to impregnatesuitable material,

such as paper, cotton, or asbestos or it has introduced therein solidmaterial in broken form such, for instance, as pearl shell chips orflakes.

The composition is then commonly dried with the to afiect the propercuring of the composition in the mold. 1

When the composition is subjected to the action of heat for drying it,the presence of the acid catalyst makes it extremely difficult tocontrol position can be obtained by partially drying a catalystcontaining urea formaldehyde product in the presence of a suitable"support", as for instance, any of the materials hereinbefore mentioned,at a normal temperature and thereafter heating the composition tocomplete the drying operation. By this partial drying operation beforethe heat is applied, the amount of water in the composition ismaterially decreased and the composition is thus rendered less sensitiveto the action of heat during. the drying operation even though acomparatively large amount of acid catalyst is present.

In practice, I take the acid catalyst containing 3 urea formaldehydecondensation product in the presence of the desired support such, forinstance, as paper, cotton, asbestos or any broken solid material aspearl shell chips or flakes, and subject the same to the action of ablast of air or other inert gas at a normal temperature, say,

below 50 C. by passing the air or other inert gas over or through thecomposition until the composition is partially dried. I thereaftersubject the partially dried composition to the action of heat tocomplete the drying operation.

The great improvement which I have noted in thecomposition byutilizingthe step of partially drying the composition at a normaltemperature and thereafter heating the composition to complete thedrying operation may arise either from the elimination of deleteriouscompounds from the composition by the air or other inert gas, or by theformation of helpful compounds because of the introduction of the air orother inert gas, at a normal temperature.

Obviously a convenient method of blowing air through the composition isto spread it on a screen or a sieve. some means of controlling thehumidity of the Itis advantageous to have air used in 'order to insureuniformity. Somesome of the heated air I0 I minimum of heat is required.Of course, the larger the volume of air or the thinner the material isspread on the screen or sieve, the shorter will be the drying time.

A detailed example of carrying out the above invention is given below.

100 lbs. of urea were dissolved in 2l8 lbs. of commercial formalinsolution containing 38% of weight of formaldehyde. After all the ureawas added the temperature dropped to 6 C. Sullicient ammonium hydroxidewas then added to give the mixture a pH value of 6.5. After bringing thetemperature to 30 C. itwas maintained there bycooling for one-half hour.The solution was then mixed or shredded with 80 lbs. of sheeted Alphafibreian absorbent and loosely compressed form of paper containing ahigh proportion of Alpha cellulose) until the sheets were broken down.The wet fibrous material was placed uniformly on a 10 mesh Monel metalscreen fitted in a dryer so that a large volume of air was forcedthrough the screen and the material. The screen was approximately 75 byinches and the volume of air blown through was roughly 2,000 cubic feeta minute. The dryer was arranged with an outlet,so that all 'or littleof the air could be re-circulated. At first air was blown through thematerial with the vent kept open so that little of the air would bere-circulated. Thus fresh dry air was blown over the materi for somehours until nearly dry. Then heat was applied to the coils through whichthe air passed, and as the drying proceeded the vents were partiallyclosed. The temperature recorded in the material varied from 30 C. atthe start until it reached as high as 50-60 C. at the finish. Care hadto be taken that the material would notget .too stiff so that it couldnot be properly molded or that the material was sufliciently dry so thatit could be properly ground without "gumming up" the mill. The pH ofdistilled water extract of the final material was found to beapproximately 6.5. Due to the presence of some material which rapidlydecomposed in the presence of water the pH value rapidly went to a pH ofroughly 8.0.

The method of taking the p1! of the molding t6 powder composition is asfollows: grams of the molding composition were mixed with cc. ofdistilled water, filtered as quickly as possible and a few drops of BromThymol Blue added to the filtrate. One minute after pouring into thefilter the filtrate gave a color showing the pI-I was 6.5; upon standingthe pH increases to 7.7 and above after ten minutes.-

Other methods of drying include vacuum, drum, or spray drying. Sincedrying and polymerization must proceed simultaneously; the method ofdrying will determine the amount of catalyst which should be used.Vacuum drying is a much faster process than drying at atmosphericpressure or at ordinary temperatures, so that therefore a greater amountof catalyst should be used. Spray drying is a still faster method andthus a still greater amount of catalyst can be used.

Instead of urea, thiourea or substitution products of urea or ofthiourea or substance from which urea or thiourea can be prepared, maybe used in so far as they are not specifically limited, all of which Iwish to be included along with urea in the designation urea used in thefollowing claims. Such substances are guanidin, cyanamid, dicyandiamid,ammonium thiocyanate and ammonium cyanate. The formaldehyde may be usedeither in the commercial aqueous solution or in the gaseous state or inthe form of a solution of anhydrous formaldehyde .or in the form of thepolymers.

Before conversion into the solid condition there can be incorporated inthe mass filling materials of fibrous, pulverulent or liquid character,or agents conferring elasticity or coloring matters.

Because of the absence of any appreciable amounts of water in theproduct before being converted into the solid condition, manyplasticizers or modifying agents are soluble in it. The advantages ofusing such a; water-free material, either with or without plastiflers ormodifying agents is set forth in my copending application No. 664,207filed April 3, 1933. In this prior application I disclose a method ofremoving water from an acid condensation product of urea andformaldehyde at a low temperature in such manner that the reaction willnot progress too far before the water is removed. By this partial dryingoperation, that is by blowing air at ordinary temperatures to partiallydry the mass before heat is applied, the amount of water inthecomposition is-materially decreased and the composition thus rendered.less sensitive to the action of heat during the drying operation eventhough a comparatively large amount of an acid catalyst is present.

Thus while I have described my improvement in detail and with respect tocertain preferred forms, I do not desire to be limited to such detailsor forms since, as will be noticed by those skilled in the art, afterunderstanding my invention many changes and modifications may be madeand the invention embodied in widely different forms without departingfrom the spirit and scope thereof in its broader aspects, and I desireto cover all modifications, forms and improvements coming within thescope of any one or more of the appended. claims.

This application is a continuation in part of applications Serial Nos.422,545, Jan. 22, 1930;

429,202, filed Feb. 17, 1930; 664,207, April 3, 1933;.

664,208, April 3, 1933.

In my application Serial No. 664,207 I disclose principally a method ofincreasing the flow of urea-formaldehyde molding compositions involvingthe introduction of a solution of urea in formaldehyde which may havebeen previously reacted or not into urea-formaldehyde molding powders.The molding compositions produced in accordance with the presentinvention may be treated in the manner of the compositions of the priorapplication.

Having thus described my invention what I claim as new and desire tosecure by Letter Patent is:

1. In the process of manufacturing urea formaldehyde condensationproducts, the steps which consists in reacting urea and formaldehyde insolution at least to the methylol urea stage but not until substantialpolymerization begins, then removing as much solvent as possible andcontinuing the reaction and drying simultaneously in the presence of anacid substance, thereby producing a fusible mass, suitable for casting,molding and the like.

2. In the process of manufacturing urea formaldehyde condensationproducts, the steps which consist in reacting urea and formaldehyde insolution no further than the formation of 'a methylol urea said formformaldehyde as such being completely reacted, and then before anyappreciable polymerization begins removing as much solvent as possibleand continuing the reaction and drying simultaneously in the presence ofan acid substance, thereby producing a fusible product.

3. In the process of manufacturing urea formaldehyde condensationproducts, the steps which consist in reacting ureav and formaldehyde insolution at least to the methylol urea stage but before there is asubstantial change in the viscosity of the solution, removing as muchsolvent as possible and continuing the reaction and dryingsimultaneously in the presence of an acid substance, thereby producing afusible product.

4. In the process of manufacturing urea formaldehyde condensationproducts, the steps which consist in removing as much solvent aspossible from a reaction product of urea and formaldehyde in solutionreacted at least to the methylol urea stage but not until appreciablepolymerization occurs, then simultaneously continuing the reaction anddrying in the presence of an acid substance, thereby producing a fusibleproduct.

5. In the process of manufacturing urea fcrmaldehyde condensationproducts from a solution of the initial reaction products of ureaandformaldehyde from which as much solvent as possible has been removed,the steps which consists in simultaneously continuing the reaction anddrying process in the presence of an acid substance thereby producing afusible product, the solution of said initial reaction product beingsubstantially free of formaldehyde as such and free of gelatinouspolymerization products.

6. In the process of manufacturing urea formaldehyde moldingcompositions, the steps which comprise drying a methylol ureacondensation product of urea and an aqueous solution of formaldehyde,the said condensation product before drying not having been reacted tothe point where there is a substantial change in the viscosity of thesolution, then simultaneously drying and continuing the reaction in thepresence of an acid and in the presence of as little water aspracticable, thereby producing a fusible molding composition.

7. In the process of manufacturing urea formaldehyde moldingcompositions, the steps which a,14o,se1

product which has been reacted at least to the comprise mixing amethylol condensation product of urea and an aqueous solution offormaldehyde having a pH value above 4, the said condensation productbefore drying is commenced not having been reacted to thepoint wherethere is a substantial change in the viscosity of the solution, mixing afiller with the solution, then simultaneously drying and continuing thereaction in the presence of an acid and in the presence of as littlewater as practicable, thereby producing a fusiblemolding composition.

8. In the process of manufacturing urea formaldehyde moldingcompositions, the steps which comprise mixing the primary reactionproduct of from more than 1.05 moles of urea and 2 moles of aqueousformaldehyde with a filler, the primary reaction product before mixinghaving been reacted at least until methylol urea is formed but nothaving beenreacted to the point where there is a substantial change inthe viscosity of the 4 solution, then simultaneously continuing thereaction and the drying, thereby producing a fusible moldingcomposition. I

9. In the process of manufacturing urea formaldehyde moldingcompositions, the steps which comprise mixing the primary reactionproduct of urea and an aqueous solution of formaldehyde with a cellulosefiller, the primary reaction product before drying having been reactedat a low temperature at least until methylol urea is formed but not sofar that the viscosity of the solution is substantially changed, thensimultaneously drying and continuing the reaction in the presence of anacid substance and in the presence of as little water as practicable,thereby producing a fusible molding composition.

10. In the process of manufacturing urea formaldehyde moldingcompositions, the steps which comprise drying the primary reactionproduct of urea and an aqueous solution of formaldehyde with a filler,the primary reaction product before drying having been reacted at leastuntil methylol urea is substantially formed but not having been reactedto the point where there is a substantial change in the viscosity of thesolution, then simultaneously continuing the reaction and the drying,thereby producing a fusible molding com- I hyde molding compositionwhich consists in blowing air at a temperature below 50 0. through acondensation product free of any polymerization of mixed with a suitablefiller, such mixture forming a porous mass permitting the passage of agas during the drying process, to partially dry the composition andthereafter blowing air at a higher temperature through the compositionin order to co1nplete the drying operation.

14. The method of drying to produce a urea formaldehyde moldingcomposition which consists in blowing air or other inert gas through asolution of a urea-formaldehyde condensate free of any polymerizationproduct thereof mixed with supporting substances, suchsubstancesactingboth to form a porous material permitting the passage of a gas duringthe drying process and also acting as-a suitable filler for the moldedproduct.

15. The method of drying to produce a urea formaldehyde-moldingcomposition which consists in blowing air or other inert gas through asieve on which is placed a solution of a ureaformaldehyde condensatereacted at least to the methylol urea stage, but to an insufficientdegree to change the viscosity of the solution to any substantialextent, said solution being in admixture with supporting substances,such substances acting both to form a'porous material permitting thepassage of a gas during the drying process and also acting as asuitable} filler for the molded product.

16. The process of manufacturing fusible ureaformaldehyde condensationproducts which comprises subjecting a solution of dimethylol urea to adrying operation in the presence of an acid catalyst, said dryingoperation serving simultaneously to advance the condensation reaction ata rate which removes most of the water present before polymerizationbegins and solidification more than 1.05 of the latter under an acid pH-value above 4, thereby forming methylol urea in solution, continuing thecondensation reaction but before any substantial polymerization occursevaporating off the water present in the presence of an acid catalyst,said acid catalyst serving to advance the reaction and hence to liberatewate of the condensation reaction.

' LEONARD BMIDIH.

cEmIrIcAT on conmscnon.

Patent No. 2,11 .0,561. December 20, 193

momma snm'rn o It is hereby certified that error appears in the printedspecification of the above numbered patent requiring correction a;follows: Page 3 first coluinn, line 5, for "1.5 1 n016s of urea with'l'mole" read 1 mole of urea with 1.5 mole; and that'the paid. Le tterePatent should be read with this correction therein that the: same mayconIorm-to the record of the, dose in the Patent 'Offioe'.

Signed manned this 18th dayof April, A. n. '19 9.

Henry Van Arsdale LSeal').

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